Dynamic access to record columns (in PL/pgsql)

Hello

I have a trigger procedure which I want to be called after insert or
update on different tables. In this procedure, I need to find the values
of key fields for the affected table in the NEW record, but I can't find
a way to access a field the name of which I only know at execution time.
I tried many workarounds, for example this:

fieldname := name of key field;
EXECUTE 'SELECT NEW.'||fieldname INTO fieldvalue;

But none of them worked. I found a one-year-old thread about this kind
of dynamic access, which proposed a syntax like this: NEW.(fieldname),
but this hasn't be implemented in the current version and, apparently,
no different methods where suggested. Can anybody suggest me how to do
that? Right now I can only think of programmatically generating one
different procedure for every table I want to track (there are 42), but
this would be very clunky solution.

Thanks for your time

Daniele Mazzini